Charging and using a Garmin Edge (500) - solutions?

I have seen it mentioned a few times on here, but not seen a solution. Can anybody recommend a way of charging my Garmin 500 while using it? I know people have talked about hacking USB cables but I am a simple man and have no skills with electronics

The 500 doesn't As soon as you connect it to a wall charger or a PC they switch off and charge. I believe you can hack a USB cable to prevent this but I don't know about that. Wondered if there was something I could buy.

surely on 10 second recording and all backlighting set to zero or minimum would see you through? They seem to last for days. On sat night I rode home for an hour 10 mins,left it running by mistake through the night and 16 hours later I was on my return trip. I still had about 40% left. Mind you, maybe it doesn't use much just sitting stationary with the timer still running as you sleep :O/